3D printed ion exchange membranes could improve energy, water purification, and more

Jun 2, 2016 | By Benedict

Penn State researchers have used a custom 3D photolithographic process similar to stereolithography to 3D print micro-patterned anion exchange membranes. The membranes, patterned for improved performance, could be used in energy, water purification, desalination, and other applications.

Although they might resemble small pieces of run-of-the-mill kitchen plastic wrap, ion exchange membranes play a vital role several different practical processes. The thin, flat polymer sheets can be used in fuel cells and batteries, while food processing, heavy metals removal, and water purification can also benefit from the membranes. While these polymer membranes have traditionally been made flat and smooth, scientists have recently found that they can instill interesting hydrodynamic properties in the polymers by creating 3D patterns on their surface.

These 3D patterns can help to improve ion transport, which is the primary function of the membranes, and can also mitigate fouling, a common problem associated with ion exchange. Unfortunately, making these 3D patterns has proved to be a relatively difficult task, necessitating the laborious process of etching a silicon mold before pouring in the polymer and waiting for it to solidify. As it happens, however, there is another kind of technology out there—more advanced even than the etching needle—which enables users to quickly and accurately create 3D structures.

A group of Penn State researchers studying anion exchange membranes—the kind used to transfer negatively charged ions instead of positively charged ions—quickly recognized that they could use 3D printing to help them create complex 3D shapes on the exchange membranes. “We thought if we could use 3D printing to fabricate our custom-synthesized ion exchange membranes, we could make any sort of pattern and we could make it quickly,” said Michael Hickner, Associate Professor of Materials Science and Engineering at Penn State.

In order to create the preicse 3D patterns, Hickner and his team used a 3D printing process similar to stereolithography, using a light projector to cure a mixture of ionic polymers for a base layer, then adding more polymer and projecting a pattern onto that new material to create a 3D surface on the membrane. According to tests carried out on the 3D printed membranes, the patterns helped to increase conductivity by a factor of two to three. “Membranes act like a resistor in a battery or fuel cell,” Hickner said. “If you can lower the resistance by a factor of two or three, you’ve really got something useful.”

While other scientists have already experimented with 3D patterns on ion exchange membranes, the Penn State researchers believe that their research represents the first use of 3D printing for this particular application. “This is the first 3D printed example of these structures and the first model that really explains the resistance decrease in a quantitative way,” said Jiho Seo, a PhD student and lead author on the paper. “A simple parallel resistance model describes the effect of the pattern on lowering the resistance of these new membranes. This insight gives us a design tool to continue to innovate and create new patterns for further improvements along with changing the intrinsic chemistry of the material.”

According to the research team, this exciting development is just the beginning. Hickner, Seo, and third member Douglas Kushner will continue to optimize the 3D geometries of the membranes in order to further improve their efficiency, while also experimenting with new materials. “We want to bridge the fundamental chemistry and materials science that we do with the engineering and rapid design iterations that the 3D printing industry is really good at,” Hickner said.

The team’s researchpaper has been published in the journal ACS Applied Materials & Interfaces.